PROJECT SUMMARY/ABSTRACT Colorectal cancer (CRC) is the second leading cause of cancer-related death in the U.S. and there has been a focused effort to understand the molecular basis of this malignancy, including its development, progression, and metastasis. Carcinogenesis is the consequence of cumulative and sequential genetic alterations. A more thorough understanding of the altered molecular pathways may contribute to improved strategies for prevention, screening, diagnosis and therapy. Genomic instability occurs when the cell is no longer capable of controlling its own mutation rate. Three separate pathways contribute to this imbalance, of which chromosomal instability (CIN) pathway is the most common, and is characterized by gains and/or losses of whole or portion of chromosomes. Among the factors that promote CIN is centrosome amplification, frequently manifested as abnormal centrosome numbers. The centrosomes are involved in a variety of cellular processes, including chromosome segregation during mitosis. Another important and life-threatening manifestation of cancer progression is metastasis, which occurs through a process involving epithelial-mesenchymal-transition (EMT). EMT allows a polarized epithelial cell to acquire a mesenchymal cell phenotype, which includes enhanced migratory capacity, invasiveness and elevated resistance to apoptosis. The full spectrum of molecular mechanisms that contribute to EMT of carcinoma cells remains unclear. The LONG-TERM GOAL of this project is to understand the molecular mechanisms responsible for the formation of colorectal cancer. The zinc finger-containing transcription factor Krppel-like factor 4 (KLF4) is expressed in the terminally differentiated intestinal epithelial cells. We have established that KLF4 is anti-proliferative and is essential for mediating the cell cycle checkpoint functions of p53 following DNA damage. KLF4 has been shown to be a potential tumor suppressor in CRC in both humans and in mouse models of intestinal tumorigenesis, and its genetic deletion results in centrosome amplification. Additionally, KLF4 was shown to be a suppressor of EMT in breast cancer cells. These findings indicate that KLF4 plays an important role in the pathogenesis of CRC, and advocates KLF4 as a potential suppressor of EMT in CRC. Based on these observations, we propose two HYPOTHESES that KLF4 (1) is a critical regulator of genomic stability and does so by regulating centrosome duplication and (2) is involved in suppressing EMT in CRC. We propose 2 SPECIFIC AIMS to test these hypotheses: (1) To determine the mechanisms by which KLF4 regulates centrosome duplication; (2) To correlate KLF4 levels with the levels of EMT markers in CRC and to determine whether KLF4 regulates EMT in CRC. These experiments will provide definitive evidence that KLF4 is a critical regulator of centrosome duplication and thus a suppressor of genetic instability in vitro and in vivo. Additionally, they will also establish KLF4 as a suppressor of EMT, and thus metastasis of colon cancer. The results will considerably advance the understanding of CRC formation and may posit KLF4 as a potential therapeutic target in colon cancer.